Human working intensity of children walking with different loads

This study determined the relative human working intensity of children walking with different loads. Fifteen male children, aged 12, were selected from a primary school to carry school bags of 10, 15 and 20% of their body weights, and no load was used as control. Maximal oxygen uptake (VO₂max) of every subject were measured on a motorized treadmill using a continuous incremental protocol. In the load carriage test, subjects walked at 1.1 m s^-1 for 20 min on a treadmill. During walking, expired gas of subjects were collected and analyzed by a cardiopulmonary function system. Based on the results of expired gas analysis, human walking intensity during walking at different load conditions were calculated and presented by the percent of VO₂max. Heart rate of subjects were monitored and recorded by electrocardiograph until 5 min after walking. Blood pressure were measured before, immediately, 3 and 5 min after every trial. There was a significant difference found on the human working intensity between 10 and 20% body weight load conditions, but not among the 0%, 10% and 15% body weight load conditions. Heart rate responses among all load conditions showed similar trends. 60% maximum heart rate was obtained at different load conditions among the subjects. It is concluded that 10% body weight is recommended as the weight of school bags for children